Coating material for the surfaces of plates

Description

[0001] The invention relates to a coating material for the surfaces of panels, in particular wood panels, wood-based panels, plastic panels or panels made from a wood-plastic mixture, wherein the coating material consists of a single resin-impregnated cellulose layer provided on one side with a decor, which is provided with a transparent top layer covering the decor made of a mixture of acrylate lacquer and polyurethane.

[0002] Similar coating materials, in which the top layer is made of a radiation-curable acrylate lacquer, are known, for example, from EP 3 351 682 A1.

[0003] Panels used in furniture manufacturing, for example, can be coated with real wood veneer, plastic film, or plastic laminate. Continuous Pressure Laminates (CPL) are high-quality decorative materials produced in continuously operating double-belt presses. They consist of a resin-impregnated decorative paper and a multi-layered backing paper made of parchment or kraft paper. These individual layers are stacked on top of each other and bonded together in a hot press using high pressure and temperature. This process reinforces the fiber structure of the papers, creating a dense material with a closed surface. Thin CPL laminates are well-suited for applications where surfaces are subject to heavy wear. The melamine resin film that forms during the production process protects the laminate and makes the panel surface durable and long-lasting.

[0004] A method for producing a high-pressure laminate is known, for example, from EP 3 296 107 A1.

[0005] It is also known to use finishing foil or wrapping film, which consists of a paper web treated with a lacquer surface. The lacquer is cured, for example, by UV lamps. The paper is not completely penetrated by the lacquer. Therefore, the surface has only a low scratch resistance.

[0006] From DE 10 2013 112 275 B4, it is known to digitally print a decorative design onto an unreinforced, white parchment paper from a roll. A UV-curing digital printing ink is used for this purpose. After printing and ink curing, the parchment paper is rewound onto a roll. In a second step, the printed roll of parchment paper is unwound and fed, together with a translucent overlay paper that becomes completely transparent after pressing, into a double-belt press. At a pressure of 15 to 25 bar and a temperature of 150 to 210 °C, the melamine resin in the overlay paper is first liquefied, then penetrates the paper layer, and finally hardens. Thus, the unreinforced printed parchment paper and the melamine-impregnated overlay paper are unwound from two separate rolls and fed into a continuously operating double-belt press.The unresin-free parchment paper used is designed with such a surface tension that aqueous inks, as commonly used in decorative gravure printing, exhibit poor to no adhesion to the parchment sheet. Therefore, a UV-curing ink must be used. The manufacturing process is highly complex. Due to the asymmetrical structure of the laminate, it is prone to curling, which complicates further processing, such as coating the panels.

[0007] Based on this, a coating material should be created that is characterized by good processability, is as thin as possible on the one hand and has high abrasion resistance on the other.

[0008] To solve the problem, a coating material according to the preamble of claim 1 is characterized in that the impregnation with synthetic resin amounts to 50 to 75% in relation to the weight of the cellulose layer.

[0009] The cellulose layer is preferably designed as a printing base paper.

[0010] According to the invention, the cover layer consists of a mixture of acrylate lacquer and polyurethane.

[0011] Preferably, the cellulose layer is designed as a printing base paper with a weight of 60 to 100 g / m², preferably 70 to 90 g / m² and particularly preferably 70 g / m².

[0012] The cellulose layer is preferably impregnated with a urea-formaldehyde resin, a melamine-formaldehyde resin, a mixture of urea-formaldehyde resin and melamine-formaldehyde resin or with a polyurethane.

[0013] A process for manufacturing a coating material is characterized by the following steps: a) Providing a cellulose layer, b) Printing a design on the surface (top side) of the cellulose layer, c) Impregnating the cellulose layer with a liquid synthetic resin in an amount based on the weight of the cellulose layer of 50% to 75%, d) Drying the impregnated cellulose layer, e) Applying a liquid topcoat of a mixture of acrylate lacquer and polyurethane to the surface (top side) printed with the design, f) Pressing the assembly consisting of the cellulose layer and the topcoat in a hot press.

[0014] Preferably, the topcoat is applied with a roller or a roller. However, it can also be sprayed on.

[0015] It is advantageous if the cover layer is dried before the structure is pressed.

[0016] The top layer then hardens completely when the structure is pressed together.

[0017] The design can be applied using analog and / or digital printing. Preferably, a water-based digital printing ink is used.

[0018] The surface opposite the decorative layer (underside) of the core-impregnated cellulose layer can also be provided with a cover layer. The cover layer preferably has a weight of 5 to 100 g / m². More preferably, the cover layer has a weight of 10 to 60 g / m² and most preferably 30 g / m².

[0019] The drying and / or curing of the impregnated cellulose layer and also the cover layer is stopped in time so that, although some residual activity remains, the cellulose layer or the printed paper can be wound up, stacked, stored and / or transported without the layers touching each other sticking together.

[0020] An embodiment of the invention will be described in more detail below: The coating material consists of a cellulose layer designed as a printing base paper with a weight of approximately 60 to 120 g / m². In contrast to parchment paper, the printing base paper has an open structure. Printing base papers are typically white or beige and therefore already provide a good printing base for a decoration. Alternatively, the printing base papers can also have a solid-color, dyed-through decoration.

[0021] A decorative design is printed onto the top side of the base paper, preferably using single-pass digital printing with water-based digital inks (CMYK or, even better, CRYK). The decorated base paper is then core-impregnated in a standard impregnation unit. Core impregnation refers to the extensive filling of the structural spaces between the cellulose fibers of the base paper. This can be achieved with urea-formaldehyde resin, melamine-formaldehyde resin, a combination of these, or polyurethane. A common polyurethane, such as a thermoset polyurethane, is used. Between 50 and 60% of the paper weight is used for core impregnation. With core impregnation, the decorated and core-impregnated paper reaches a weight of approximately 100 g / m².

[0022] At least on the decorated side of the core-impregnated printing base paper, a topcoat is subsequently rolled or sprayed on, having a weight of approximately 5 to 100 g / m². In a non-inventive embodiment, the topcoat consists of a conventional acrylic lacquer, which can be partially cured and / or fully cured by means of high-energy radiation, e.g., UV radiation. According to the invention, however, a mixture of acrylic lacquer and polyurethane is used.

[0023] The printing base paper, coated with the partially cured varnish, is pressed in a short-cycle press or a continuous hot press at a pressure of approximately 30 to 70 N / cm² and a temperature of 130 to 200 °C. Preferably, a pressure of 60 N / cm² and a temperature of 150 °C are used. The pressing time is approximately 0.6 to 2 s / mm (sheet thickness), preferably 1.2 s / mm. The temperature in the press is measured at the surface of the pressing plate.

[0024] To ensure that some reactivity remains and that the impregnated paper can be wound, stacked, stored and / or transported, the drying and / or curing of both the core impregnation and the cover layer is stopped in time.

[0025] When a short-cycle press is used to produce the coating material, the core impregnation typically contains only polyurethane and consists mainly of urea and / or melamine-formaldehyde resin. In this case, the coating material is primarily intended for use on furniture surfaces. Of course, when using short-cycle presses, it must be ensured that they can generate sufficiently high pressing pressures.

[0026] The surface of the coating layer can be structured, as described, for example, in EP 3 296 107 A1. The structuring element is then inserted between the press plate and the structure to be laminated. It remains there during lamination and is subsequently removed from the structured surface. Particularly advantageous is the production of so-called nano- or microstructures, which facilitate cleaning of the coating material's surface and also counteract fingerprints (anti-fingerprint). The application of microfolding with an excimer lamp has proven particularly suitable for the anti-fingerprint effect. The following principle underlies microfolding: 172 nm radiation generates free radicals in acrylates, triggering polymerization and cross-linking.The penetration depth of the 172 nm photons into the acrylates is between 0.1 and 0.5 nm, so only a thin surface layer is cross-linked. The shrinkage caused by polymerization then leads to microstructures. A wrinkled skin floats on the liquid film, which is then completely cured with a second radiation source. A mercury UV lamp, an electron beam lamp, or a long-wavelength excimer lamp with 308 nm can be used for this purpose. To prevent ozone formation, the irradiation usually takes place in a nitrogen atmosphere. A method for adjusting the gloss level of decorative and functional surfaces is described, for example, in DE 10 2006 042 063 A1.

[0027] High-gloss surfaces can also be achieved by using high-gloss press strips or press plates.

[0028] Instead of using a structuring device, the press strips and / or press plates can also be structured. Preferably, the structures are at least partially synchronized with the decor, with complete synchronization being the goal.

[0029] Due to the single-layer structure of the coating material, it is very thin, which offers a great advantage in further processing, enabling even modern small radii < 1.0 mm to be reliably coated.

[0030] Continuous pressing can be carried out, for example, with a double-belt press, such as the one used by Hymmen for the production of HPL laminates. This press operates on the isobaric principle. Adjustment to the product thickness is achieved by a fixed lower and an upper, height-adjustable pressure frame. To protect the product from premature exposure to temperatures without pressure in the press, cooling zones are installed at the inlet of the double-belt press to prevent pre-reaction of the material. The raw material is pressed by the two circulating steel belts, which pass through common heating and pressing zones. In the pressing zones, the required surface pressure for the process is generated against the steel belts and thus against the material by gaseous pressurizing agents. The heat energy is generated by a thermal oil system.Separately controlled circuits of heat transfer oil bring the belt drums and the upper and lower heating plates to the required temperature. The surface pressure in the reaction zone is generated by compressed air cushions that press against the steel belts. This eliminates friction between the steel belts and the heating plate. The required pressure is generated by high-pressure compressors and supplied to the double-belt press via special pressure regulators.

[0031] Instead of a double belt press, a C-HPL hot press or a short cycle press can also be used, for example.

Claims

1. A coating material for the surfaces of panels, especially panels made of wood, wood-based material, plastic or a wood / plastic mixed material, comprised of a single resin-impregnated cellulose layer with a decor on one side, said layer being equipped with a transparent cover layer that covers the decor made of an acrylate lacquer and polyuethan, characterised in that the impregnation with synthetic resin is 50 to 75% in relation to the weight of the cellulose layer.

2. The coating material according to one of the preceding claims, characterised in that the cellulose layer is made as a print base paper with a weight of 60 to 120 g / m2, preferably 70 to 90 g / m2, especially preferably 70 g / m2.

3. The coating material according to one of the preceding layers, characterised in that the cellulose layer is impregnated with a urea-formaldehyde resin, a melamine-formaldehyde resin, a mixture of urea-formaldehyde resin and melamine-formaldehyde resin or with a polyurethane.

4. The coating material according to one of the preceding claims, characterised in that the impregnation with synthetic resin is 75% in relation to the weight of the cellulose layer.

5. A method for producing a coating material, comprising the following steps: a) providing a cellulose layer, b) printing a decor onto a surface of the cellulose layer, c) impregnating the cellulose layer with a liquid synthetic resin in a quantity of 50 to 75% in relation to the weight of the cellulose layer, d) drying the impregnated cellulose layer, e) applying a liquid cover layer made of a mixture of an acrylate lacquer and polyurethan to the surface with the printed decor, f) pressing the resulting structure composed of the cellulose layer and the cover layer in a hot press.

6. The method according to claim 5, characterised in that the cover layer is applied with a drum or a roller.

7. The method according to claim 5, characterised in that the cover layer is sprayed on.

8. The method according to one of the claims 5 to 7, characterised in that cover layer is dried before pressing the resulting structure.

9. The method according to claim 5, characterised in that the decor is printed on by analogue and / or digital printing.

10. The method according to claim 9, characterised in that a water-based digital printing ink is used.

11. The method according to on of the claims 5 to 10, characterized in that for the impregnation with synthetic resin an amount of 75% in relation to the weight of the cellulose layer is used.